1. Field of the Invention
This invention relates to illumination devices and, more particularly, to controlling illumination devices.
2. Description of Related Art
A wide variety of lighting control systems are currently commercially available for controlling a variety of lighting features from simple on/off switching to complex color adjustment and performance monitoring. Such systems also communicate according to a wide variety of protocols over various communication channels. As an example, a simple system could be just a triac dimmer and a single lamp. As another example, a complex system could be a hierarchical campus wide network. In such a complex system, up to 64 intelligent fluorescent lamp ballasts within a room or group of rooms could be wired together using the Digital Addressable Lighting Interface (DALI) standard, for instance, with an Ethernet enabled DALI controller, which then communicates with other DALI controllers and a computer server over Ethernet within each building. At the top layer of the hierarchy, the computer servers in different buildings within a campus could communicate over the Internet using Internet Protocol (IP).
Some lighting control systems use protocols that are somewhat specific to lighting, such as 0-10V, DMX512, DALI, and Dynalite, while others use protocols that target building automation in general, such as X10, LonWorks, C-Bus, and ZigBee. Still other lighting control systems use industry standard networking protocols such as Ethernet, Wi-Fi, and HomePlug. At the campus wide level with communication over the Internet, such complex lighting control systems can also use telecom networking protocols such as SONET and ATM. All theses standards and protocols communicate at different rates, using different modulation and packetizing schemes, over various communication channels. Such channels include powerline for X10 and HomePlug, RF for ZigBee and Wi-Fi, optical fiber for SONET, and dedicated wires for most of the others including 2 wire DC for 0-10V, twisted pair for DALI and others, and CAT5 for Ethernet.
The 0-10V standard was one of the earliest and simplest lighting control signaling system, which is still supported by many fluorescent ballasts produced by companies such as GE, Philips, and Sylvania. Such ballasts produce light from an attached fluorescent lamp that is proportional to the DC voltage input to the ballast through two wires. Although simple to understand and implement, each ballast must have a dedicated cable to the system controller, which can become very expensive and cumbersome in large installations. Additionally, such a lighting control system can only control light level and cannot extract information from the ballast, such as if a bulb has burned out.
The DMX512 stands for “Digital Multiplex with 512 pieces of information” and is a standard for digital communication commonly used in theaters and production studios. DMX512 communicates over shielded twisted pair cable using EIA-485 standard voltages levels with node connected together in a daisy chain manner. Data is sent one byte per packet at 250 kbaud in a manner similar to RS232. The DMX512 protocol is popular for stage lighting due to the robustness of its cable and the relatively long communication distances.
The DALI standard, which is becoming relatively popular for commercial lighting systems, is similar to DMX512 in that various lamps can be individually controlled using a relatively low data rate digital control bus, however, there are many differences ranging from the type of communication cable and interconnections to data format and messaging requirements. While DMX512 communicates uni-directionally over shielded twisted pair cable between two nodes, DALI communicates bi-directionally over un-shielded twisted pair that can be tapped by up to 64 devices. While all DMX512 data frame comprise one start bit, 8 data bits, and two stop bits, DALI has different sized frames for communication in the different directions with both acknowledge and data bytes in one direction and no acknowledge in the other direction.
Unlike DALI, DMX512, 0-10v, and other protocols developed specifically for lighting, X10 was developed for general home automation of which lighting is an important subset. A further substantial difference is that X10 typically communicates data over the power lines that are already connected to most devices. X10 devices typically communicate one bit of information around each zero crossing of a 50 or 60 Hz AC mains cycle, by coupling bursts of a high frequency signal onto the powerline. As such, the data rate is very low. To compensate, the protocol is very simple in which all packets consist of an 8 bit address and a 4 bit command. Since only 16 commands are possible, functionality is limited.
HomePlug is another protocol that uses the power line for communication, however, unlike X10, which was architected for home automation, HomePlug was designed to allow products communicate with each other and the Internet through existing home electrical wiring. A variety of versions of HomePlug have been released with data rates ranging from 10 to 200 Mbit/s. HomePlug achieves such data rates using adaptive modulation and complex error correction algorithms on over a thousand Orthogonal Frequency Division Multiplexed (OFDM) sub-carriers.
Data in a HomePlug network is typically communicated in Ethernet compatible packets, which comprise of a header with about 22 bytes, the payload with up to 1500 bytes, and a CRC code with 4 bytes, however, HomePlug also provides a variety of higher level services that provide, among other things, guaranteed delivery, fixed latency, quasi-error free service, and jitter control. As such, a HomePlug interface is much more complicated than is needed for simply lighting control.
Although communication over a power line is a good solution for some building networking applications, there are some drawbacks. For instance, there can be excessive attenuation between different phases of typically three phase systems, which can be overcome by active repeaters or sometimes with special capacitors. Additionally, signals can propagate through the power line between different buildings causing interference and security concerns. When appliances turn on and off significant noise is generated that can corrupt transmission. HomePlug physical layer interfaces have overcome some of such issues at the expense of complex analog and digital signal processing.
LonWorks is a building automation protocol that typically uses either twisted pair cable at 78 kbit/sec or the power line at a few kilobits per second for the communication channel. For communication over the power line, LonWorks uses dual carrier frequency operation in which messages are sent using one carrier frequency and, if a response is not received, the message is sent a second time using a second carrier frequency. More recent releases of the protocol allow IP data frames to be communicated across a LonWorks network, and a library of commands for a wide variety of appliances and functions have been and continue to be developed for a range of residential and commercial applications.
The C-Bus Protocol targets home automation systems as well as commercial lighting systems. Unlike the X10 protocol, C-Bus typically uses dedicated CAT5 cables and is considered by some to be more robust as a result. Ethernet also typically uses CAT5 cable for communicating between devices in a star topology with a router or switch at the center. Common data rates include 10, 100, and 1000 Mbit/sec, which are all deployed widely worldwide for computer networking. As mentioned previously, Ethernet data frames comprise a header of typically 22 bytes, a payload of up to 1500 bytes, and a CRC of four bytes. In many applications, the payload of an Ethernet frame is an Internet Protocol (IP) packet. Although overkill for simple lighting systems, Ethernet comprises the backbone of a variety of building lighting control networks, such as those from LumEnergi and others.
ZigBee comprises a group of high level communication protocols that typically use the IEEE 802.15.4-2003 standard for Wireless Personal Area Networks (WPANs) as the physical layer. As such, ZigBee typically uses small low power radios to communicate between appliances, light switches, consumer electronic, and other devices in a residence for instance. IEEE 802.15.4 uses either the 868 MHz, 915 MHz, or 2.4 GHz radio frequency bands. Data is direct-sequence spread spectrum coded and then Binary Phase Shift Key (BPSK) or Orthogonal Quadrature Phase Shift Key (OQPSK) modulated prior to transmission. Data is communicated in one of four different types of frames with variable data payload. Such frames include beacon frames, which specify a super-frame structure similar to that of HomePlug, data frames used for transfers of data, acknowledge frames used for confirming reception, and MAC command frame used for controlling the network. The SuperFrame structure allows certain devices guaranteed bandwidth and provides shared bandwidth for other devices. Many aspects of the network enable very low power communication with battery powered devices.
Wi-Fi or 802.11 is a very common wireless network for data communication between computers. A number of versions of the protocol including 802.11a, 802.11b, and 802.11g have been released over the years. The recent version, 802.11g, operates at the 2.4 GHz band and uses Orthogonal Frequency Division Multiplexing (OFDM) and typically achieves about 22 Mbit/sec average throughput. Similar to Ethernet, Wi-Fi frames comprise of a header, payload, and CRC. Similar to 802.15.4, Wi-Fi has a variety of different types of frames for communication management. In general, Internet Protocol (IP) and the associated Transport Control Protocol (TCP) run over Wi-Fi networks.
Although wireless protocols such as ZigBee and Wi-Fi do not need dedicated wires to communicate between devices, nor do they have the limitation previously mentioned associated with power line communication, such wireless networks can be limited by congestion in the increasingly crowded RF spectrum. Additionally, different countries in the world allocate spectrum differently which forces devices to sometimes operate in different frequency bands.